[css-grid-3][masonry] Create new section for repeat() notation

Author: fantasai

css-grid-3/Overview.bs

@@ -570,6 +570,26 @@ Subgrids</h3>
 		results in the subgrid getting [=masonry layout=] in its [=inline axis=].
 	</div>
 
+<h3 id="repeat-notation">
+Track Repetition: the ''repeat()'' notation</h3>
+
+	This specification introduces new keywords and masonry-specific behavior
+	for the ''repeat()'' notation.
+
+<h4 id="repeat-auto-fit">
+repeat(auto-fit)</h3>
+
+	''grid-template-rows/repeat(auto-fit)'' behaves as ''grid-template-rows/repeat(auto-fill)''
+	when the other axis is a [=masonry axis=].
+	The reason for this is that ''grid-row/auto''-placed items depend
+	on the layout size of their siblings.
+	Removing empty tracks after layout wouldn't be possible in most cases
+	since it might affect any intrinsic track sizes.
+	Even if all track sizes are definite,
+	the containing block size could change for grid-aligned absolutely-positioned descendants.
+	This makes ''grid-template-rows/repeat(auto-fit)''
+	impossible to support in a [=grid container=] with [=masonry layout=].
+
 <h3 id="track-sizing">
 Grid Axis Track Sizing</h3>
 
@@ -622,20 +642,6 @@ Grid Axis Track Sizing</h3>
 	or all items are the same size
 	(or matching multiples of that size, in the case of spanning items).
 
-<h4 id="repeat-auto-fit">
-repeat(auto-fit)</h3>
-
-	''grid-template-rows/repeat(auto-fit)'' behaves as ''grid-template-rows/repeat(auto-fill)''
-	when the other axis is a [=masonry axis=].
-	The reason for this is that ''grid-row/auto''-placed items depend
-	on the layout size of their siblings.
-	Removing empty tracks after layout wouldn't be possible in most cases
-	since it might affect any intrinsic track sizes.
-	Even if all track sizes are definite,
-	the containing block size could change for grid-aligned absolutely-positioned descendants.
-	This makes ''grid-template-rows/repeat(auto-fit)''
-	impossible to support in a [=grid container=] with [=masonry layout=].
-
 <h2 id="masonry-track-placement">
 Masonry Placement</h3>